docs: explain how to use the ghcr image (#181)

Author: avivace

README.md

@@ -32,25 +32,25 @@ mdbook watch
 
 #### Using Docker
 
-If you have [Docker installed](https://docs.docker.com/engine/install/), you can build the Docker image with:
-
-```sh
-docker build -t gb-asm-tutorial .
-```
-
-Then run the image with:
+If you have [Docker installed](https://docs.docker.com/engine/install/), you can pull and run the prebuilt image for this project:
 
 ```sh
 docker run -p 3000:3000 \
   --mount "type=bind,source=$(pwd)/preproc,target=/code/preproc" \
   --mount "type=bind,source=$(pwd)/renderer,target=/code/renderer" \
   --mount "type=bind,source=$(pwd)/src,target=/code/src" \
   --mount "type=bind,source=$(pwd)/theme,target=/code/theme" \
-  -it gb-asm-tutorial
+  -it ghcr.io/gbdev/gb-asm-tutorial
 ```
 
 That's it! gb-asm-tutorial is live at [localhost:3000](https://localhost:3000).
 
+If you prefer to build the image yourself:
+
+```sh
+docker build -t gb-asm-tutorial .
+```
+
 ## Translating
 
 To help translate the tutorial, join the [project on Crowdin](https://crowdin.com/project/gb-asm-tutorial).